Method of manufacturing a semiconductor device and a semiconductor device

ABSTRACT

In a method of manufacturing a semiconductor device, a fin structure, in which first semiconductor layers and second semiconductor layers are alternately stacked, is formed. A sacrificial gate structure is formed over the fin structure. A source/drain region of the fin structure, which is not covered by the sacrificial gate structure, is etched, thereby forming a source/drain space. The first semiconductor layers are laterally etched through the source/drain space. An inner spacer made of a dielectric material is formed on an end of each of the etched first semiconductor layers. A source/drain epitaxial layer is formed in the source/drain space to cover the inner spacer. A lateral end of each of the first semiconductor layers has a V-shape cross section after the first semiconductor layers are laterally etched.

TECHNICAL FIELD

The disclosure relates to method of manufacturing semiconductorintegrated circuits, and more particularly to method of manufacturingsemiconductor devices including fin field effect transistors (FinFETs)and/or gate-all-around (GAA) FETs, and semiconductor devices.

BACKGROUND

As the semiconductor industry has progressed into nanometer technologyprocess nodes in pursuit of higher device density, higher performance,and lower costs, challenges from both fabrication and design issues haveresulted in the development of three-dimensional designs, such as amulti-gate field effect transistor (FET), including a fin FET (Fin FET)and a gate-all-around (GAA) FET. In a Fin FET, a gate electrode isadjacent to three side surfaces of a channel region with a gatedielectric layer interposed therebetween. Because the gate structuresurrounds (wraps) the fin on three surfaces, the transistor essentiallyhas three gates controlling the current through the fin or channelregion. Unfortunately, the fourth side, the bottom part of the channelis far away from the gate electrode and thus is not under close gatecontrol. In contrast, in a GAA FET, all side surfaces of the channelregion are surrounded by the gate electrode, which allows for fullerdepletion in the channel region and results in less short-channeleffects due to steeper sub-threshold current swing (SS) and smallerdrain induced barrier lowering (DIBL). As transistor dimensions arecontinually scaled down to sub 10-15 nm technology nodes, furtherimprovements of the GAA FET are required.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detaileddescription when read with the accompanying figures. It is emphasizedthat, in accordance with the standard practice in the industry, variousfeatures are not drawn to scale and are used for illustration purposesonly. In fact, the dimensions of the various features may be arbitrarilyincreased or reduced for clarity of discussion.

FIGS. 1A-1D show various views of a semiconductor FET device accordingto an embodiment of the present disclosure. FIG. 1A is a cross sectionalview along the X direction (source-drain direction), FIG. 1B is a crosssectional view corresponding to Y1-Y1 of FIG. 1A, FIG. 1C is a crosssectional view corresponding to Y2-Y2 of FIG. 1A and FIG. 1D shows across sectional view corresponding to Y3-Y3 of FIG. 1A.

FIGS. 2A-2D show various views of a semiconductor FET device accordingto an embodiment of the present disclosure. FIG. 2A is a cross sectionalview along the X direction (source-drain direction), FIG. 2B is a crosssectional view corresponding to Y1-Y1 of FIG. 2A, FIG. 2C is a crosssectional view corresponding to Y2-Y2 of FIG. 2A and FIG. 2D shows across sectional view corresponding to Y3-Y3 of FIG. 2A.

FIGS. 3A-3D show various views of a semiconductor FET device accordingto an embodiment of the present disclosure. FIG. 3A is a cross sectionalview along the X direction (source-drain direction), FIG. 3B is a crosssectional view corresponding to Y1-Y1 of FIG. 3A, FIG. 3C is a crosssectional view corresponding to Y2-Y2 of FIG. 3A and FIG. 3D shows across sectional view corresponding to Y3-Y3 of FIG. 3A.

FIGS. 4A-4D show various views of a semiconductor FET device accordingto an embodiment of the present disclosure. FIG. 4A is a cross sectionalview along the X direction (source-drain direction), FIG. 4B is a crosssectional view corresponding to Y1-Y1 of FIG. 4A, FIG. 4C is a crosssectional view corresponding to Y2-Y2 of FIG. 1A and FIG. 4D shows across sectional view corresponding to Y3-Y3 of FIG. 4A.

FIGS. 5A and 5B show one of the various stages of manufacturing asemiconductor GAA FET device according to an embodiment of the presentdisclosure.

FIGS. 6A and 6B show one of the various stages of manufacturing asemiconductor GAA FET device according to an embodiment of the presentdisclosure.

FIGS. 7A and 7B show one of the various stages of manufacturing asemiconductor GAA FET device according to an embodiment of the presentdisclosure. FIG. 7A shows a cross sectional view for an n-type GAA FET,and FIG. 7B shows a cross sectional view for a p-type GAA FET.

FIGS. 8A, 8B and 8C show one of the various stages of manufacturing asemiconductor GAA FET device according to an embodiment of the presentdisclosure. FIG. 8A shows a cross sectional view for an n-type GAA FET,and FIG. 8B shows a cross sectional view for a p-type GAA FET. FIG. 8Cis a perspective view for an n-type GAA FET.

FIGS. 9A and 9B show one of the various stages of manufacturing asemiconductor GAA FET device according to an embodiment of the presentdisclosure. FIG. 9A shows a cross sectional view for an n-type GAA FET,and FIG. 9B shows a cross sectional view for a p-type GAA FET.

FIGS. 10A and 10B show one of the various stages of manufacturing asemiconductor GAA FET device according to an embodiment of the presentdisclosure. FIG. 10A shows a cross sectional view for an n-type GAA FET,and FIG. 10B shows a cross sectional view for a p-type GAA FET.

FIGS. 11A and 11B show one of the various stages of manufacturing asemiconductor GAA FET device according to an embodiment of the presentdisclosure. FIG. 11A shows a cross sectional view for an n-type GAA FET,and FIG. 11B shows a cross sectional view for a p-type GAA FET.

FIGS. 12A and 12B show one of the various stages of manufacturing asemiconductor GAA FET device according to an embodiment of the presentdisclosure. FIG. 12A shows a cross sectional view for an n-type GAA FET,and FIG. 12B shows a cross sectional view for a p-type GAA FET.

FIGS. 13A and 13B show one of the various stages of manufacturing asemiconductor GAA FET device according to an embodiment of the presentdisclosure. FIG. 13A shows a cross sectional view for an n-type GAA FET,and FIG. 13B shows a cross sectional view for a p-type GAA FET.

FIGS. 14A and 14B show one of the various stages of manufacturing asemiconductor GAA FET device according to an embodiment of the presentdisclosure. FIG. 14A shows a cross sectional view for an n-type GAA FET,and FIG. 14B shows a cross sectional view for a p-type GAA FET.

FIGS. 15A and 15B show one of the various stages of manufacturing asemiconductor GAA FET device according to an embodiment of the presentdisclosure. FIG. 15A shows a cross sectional view for an n-type GAA FET,and FIG. 15B shows a cross sectional view for a p-type GAA FET.

FIGS. 16A and 16B show one of the various stages of manufacturing asemiconductor GAA FET device according to an embodiment of the presentdisclosure. FIG. 16A shows a cross sectional view for an n-type GAA FET,and FIG. 16B shows a cross sectional view for a p-type GAA FET.

FIGS. 17A and 17B show one of the various stages of manufacturing asemiconductor GAA FET device according to an embodiment of the presentdisclosure. FIG. 17A shows a cross sectional view for an n-type GAA FET,and FIG. 17B shows a cross sectional view for a p-type GAA FET.

FIGS. 18A and 18B show one of the various stages of manufacturing asemiconductor GAA FET device according to an embodiment of the presentdisclosure. FIG. 18A shows a cross sectional view for an n-type GAA FET,and FIG. 18B shows a cross sectional view for a p-type GAA FET.

FIGS. 19A and 19B show one of the various stages of manufacturing asemiconductor GAA FET device according to an embodiment of the presentdisclosure. FIG. 19A shows a cross sectional view for an n-type GAA FET,and FIG. 19B shows a cross sectional view for a p-type GAA FET.

FIGS. 20A and 20B show one of the various stages of manufacturing asemiconductor GAA FET device according to an embodiment of the presentdisclosure. FIG. 20A shows a cross sectional view for an n-type GAA FET,and FIG. 20B shows a cross sectional view for a p-type GAA FET.

FIGS. 21A and 21B show one of the various stages of manufacturing asemiconductor GAA FET device according to another embodiment of thepresent disclosure. FIG. 21A shows a cross sectional view for an n-typeGAA FET, and FIG. 21B shows a cross sectional view for a p-type GAA FET.

FIGS. 22A and 22B show one of the various stages of manufacturing asemiconductor GAA FET device according to another embodiment of thepresent disclosure. FIG. 22A shows a cross sectional view for an n-typeGAA FET, and FIG. 22B shows a cross sectional view for a p-type GAA FET.

FIGS. 23A and 23B show one of the various stages of manufacturing asemiconductor GAA FET device according to another embodiment of thepresent disclosure. FIG. 23A shows a cross sectional view for an n-typeGAA FET, and FIG. 23B shows a cross sectional view for a p-type GAA FET.

FIGS. 24A and 24B show one of the various stages of manufacturing asemiconductor GAA FET device according to another embodiment of thepresent disclosure. FIG. 24A shows a cross sectional view for an n-typeGAA FET, and FIG. 24B shows a cross sectional view for a p-type GAA FET.

FIGS. 25A and 25B show one of the various stages of manufacturing asemiconductor GAA FET device according to another embodiment of thepresent disclosure. FIG. 25A shows a cross sectional view for an n-typeGAA FET, and FIG. 25B shows a cross sectional view for a p-type GAA FET.

FIGS. 26A and 26B show one of the various stages of manufacturing asemiconductor GAA FET device according to another embodiment of thepresent disclosure. FIG. 26A shows a cross sectional view for an n-typeGAA FET, and FIG. 26B shows a cross sectional view for a p-type GAA FET.

FIGS. 27A and 27B show one of the various stages of manufacturing asemiconductor GAA FET device according to another embodiment of thepresent disclosure. FIG. 27A shows a cross sectional view for an n-typeGAA FET, and FIG. 27B shows a cross sectional view for a p-type GAA FET.

FIGS. 28A and 28B show one of the various stages of manufacturing asemiconductor GAA FET device according to another embodiment of thepresent disclosure. FIG. 28A shows a cross sectional view for an n-typeGAA FET, and FIG. 28B shows a cross sectional view for a p-type GAA FET.

FIGS. 29A and 29B show one of the various stages of manufacturing asemiconductor GAA FET device according to another embodiment of thepresent disclosure. FIG. 29A shows a cross sectional view for an n-typeGAA FET, and FIG. 29B shows a cross sectional view for a p-type GAA FET.

FIGS. 30A and 30B show one of the various stages of manufacturing asemiconductor GAA FET device according to another embodiment of thepresent disclosure. FIG. 30A shows a cross sectional view for an n-typeGAA FET, and FIG. 30B shows a cross sectional view for a p-type GAA FET.

FIGS. 31A and 31B show one of the various stages of manufacturing asemiconductor GAA FET device according to another embodiment of thepresent disclosure. FIG. 31A shows a cross sectional view for an n-typeGAA FET, and FIG. 31B shows a cross sectional view for a p-type GAA FET.

FIGS. 32A and 32B show one of the various stages of manufacturing asemiconductor GAA FET device according to another embodiment of thepresent disclosure. FIG. 32A shows a cross sectional view for an n-typeGAA FET, and FIG. 32B shows a cross sectional view for a p-type GAA FET.

DETAILED DESCRIPTION

It is to be understood that the following disclosure provides manydifferent embodiments, or examples, for implementing different featuresof the invention. Specific embodiments or examples of components andarrangements are described below to simplify the present disclosure.These are, of course, merely examples and are not intended to belimiting. For example, dimensions of elements are not limited to thedisclosed range or values, but may depend upon process conditions and/ordesired properties of the device. Moreover, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed interposing the first and second features, suchthat the first and second features may not be in direct contact. Variousfeatures may be arbitrarily drawn in different scales for simplicity andclarity.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly. In addition, the term“being made of” may mean either “comprising” or “consisting of.” In thepresent disclosure, a phrase “one of A, B and C” means “A, B and/or C”(A, B, C, A and B, A and C, B and C, or A, B and C), and does not meanone element from A, one element from B and one element from C, unlessotherwise described.

Generally, it is difficult to control lateral etching amounts when thenanowires (NWs) are released by selectively etching sacrificialsemiconductor layers. The lateral ends of the NWs may be etched when theNW release etching process is performed after a dummy polysilicon gateis removed, because a lateral etching control or an etching budget forNW release etch is not sufficient. A gate electrode may touch asource/drain (source/drain) epitaxial layer if there is no etch stoplayer. Further, there is a lager impact on gate to drain capacitance(Cgd). If no dielectric film existed between the gate and thesource/drain region, Cgd becomes larger, which would reduce circuitspeed.

Further, in a GAA FET, an inner spacer is provided between a metal gateelectrode and a source/drain (source/drain) epitaxial layer. However, itis difficult to uniformly form inner spacers due to process variationsnot only in each device but also within the overall wafer and/orwafer-to-wafer. Further, it is necessary to provide better gate controlfor a GAA FET having inner spacers. The inner spacers act as an extrasource of channel resistance, thereby hindering the gate controlcapability. A higher channel height in a GAA FET causes moredifficulties in deposition and etching processes to more preciselycontrol a uniformity of the structure from the channel bottom to thechannel top. In particular, achieving a higher process uniformity withina 12-inch wafer becomes more difficult in a GAA FET fabrication method.

In the present disclosure, a novel method for fabricating an innerspacer between a metal gate electrode and a source/drain (source/drain)epitaxial layer for a GAA FET and a stacked channel FET are provided. Inparticular, in the present disclosure, the inner space has a wedge-shapecross section (triangular shape) defined by a (111) facet of asemiconductor crystal. In the present disclosure, the inner spacers canbe more uniformly formed by a self-limited etch stop property. Byemploying a wedge-shape or a triangle shape inner spacer, it is possibleto make more space for a gate dielectric layer and a gate electrode,thereby improving the gate control capability.

In this disclosure, a source/drain refers to a source and/or a drain. Itis noted that in the present disclosure, a source and a drain areinterchangeably used and the structures thereof are substantially thesame.

FIGS. 1A-1D show various views of a semiconductor GAA FET deviceaccording to an embodiment of the present disclosure. FIG. 1A is a crosssectional view along the X direction (source-drain direction), FIG. 1Bis a cross sectional view corresponding to Y1-Y1 of FIG. 1A, FIG. 1C isa cross sectional view corresponding to Y2-Y2 of FIG. 1A and FIG. 1Dshows a cross sectional view corresponding to Y3-Y3 of FIG. 1A.

As shown in FIGS. 1A-1C, semiconductor wires 25 are provided over asemiconductor substrate 10, and vertically arranged along the Zdirection (the normal direction of the principal surface of thesubstrate 10). In some embodiments, the substrate 10 includes a singlecrystalline semiconductor layer on at least it surface portion. Thesubstrate 10 may comprise a single crystalline semiconductor materialsuch as, but not limited to Si, Ge, SiGe, GaAs, InSb, GaP, GaSb, InAlAs,InGaAs, GaSbP, GaAsSb and InP. In certain embodiments, the substrate 10is made of crystalline Si.

The substrate 10 may include in its surface region, one or more bufferlayers (not shown). The buffer layers can serve to gradually change thelattice constant from that of the substrate to that of the source/drainregions. The buffer layers may be formed from epitaxially grown singlecrystalline semiconductor materials such as, but not limited to Si, Ge,GeSn, SiGe, GaAs, InSb, GaP, GaSb, InAlAs, InGaAs, GaSbP, GaAsSb, GaN,GaP, and InP. In a particular embodiment, the substrate 10 comprisessilicon germanium (SiGe) buffer layers epitaxially grown on the siliconsubstrate 10. The germanium concentration of the SiGe buffer layers mayincrease from 30 atomic % germanium for the bottom-most buffer layer to70 atomic % germanium for the top-most buffer layer.

As shown in FIGS. 1A-1C, the semiconductor wires 25, which are channellayers, are disposed over the substrate 10. In some embodiments, thesemiconductor wires 25 are disposed over a fin structure 11 (see, FIG.5) protruding from the substrate 10. Each of the channel layers 25 iswrapped around by a gate dielectric layer 82 and a gate electrode layer84. The thickness of the semiconductor wires 25 is in a range from about5 nm to about 15 nm and the width of the semiconductor wires 25 is in arange from about 5 nm to about 15 nm in some embodiments. In someembodiments, the gate dielectric layer 82 includes an interfacial layerand a high-k dielectric layer. The gate structure includes the gatedielectric layer 82, the gate electrode layer 84 and sidewall spacers40. Although FIGS. 1A-1C show four semiconductor wires 25, the number ofthe semiconductor wires 25 is not limited to four, and may be as smallas one or more than four, and may be up to ten. By adjusting the numbersof the semiconductor wires, a driving current of the GAA FET device canbe adjusted.

Further, a source/drain epitaxial layer 50 is disposed over thesubstrate 10. The source/drain epitaxial layer 50 is in direct contactwith end faces of the channel layer 25, and is separated by insulatinginner spacers 35 and the gate dielectric layer 82 from the gateelectrode layer 84. In some embodiments, an additional insulating layer(not shown) is conformally formed on the inner surface of the spacerregions. As shown FIG. 1A, the cross section along the X direction ofthe inner spacer 35 has a wedge-shape or a substantially triangularshape.

An interlayer dielectric (ILD) layer 70 is disposed over thesource/drain epitaxial layer 50 and a conductive contact layer 72 isdisposed on the source/drain epitaxial layer 50, and a conductive plug75 passing though the ILD layer 70 is disposed over the conductivecontact layer 72. The conductive contact layer 72 includes one or morelayers of conductive material. In some embodiments, the conductivecontact layer 72 includes a silicide layer, such as WSi, NiSi, TiSi orCoSi or other suitable silicide material or an alloy of a metal elementand silicon and/or germanium.

FIGS. 2A-2D show various views of a semiconductor FET device accordingto another embodiment of the present disclosure. FIG. 2A is a crosssectional view along the X direction (source-drain direction), FIG. 2Bis a cross sectional view corresponding to Y1-Y1 of FIG. 2A, FIG. 2C isa cross sectional view corresponding to Y2-Y2 of FIG. 2A and FIG. 2Dshows a cross sectional view corresponding to Y3-Y3 of FIG. 2A.Material, configuration, dimensions and/or processes the same as orsimilar to the foregoing embodiments described with respect to FIGS.1A-1D may be employed in the embodiment of FIGS. 2A-2D, and detailedexplanation thereof may be omitted.

In this embodiment, the source/drain epitaxial layer 50 wraps around endportions of the semiconductor wires 25 disposed at the source/drainregions, or the semiconductor wires 25 pass through the source/drainepitaxial layer 50.

In the embodiments of FIGS. 1A-1D and 2A-2D, the GAA FET is an n-typeGAA FET. The semiconductor wires 25 are made of Si or Si_(1-x)Ge_(x),where x is equal to or less than 0.2. The source/drain epitaxial layer50 is made of one or more of Si, SiP, SiC or SiCP.

FIGS. 3A-3D show various views of a semiconductor FET device accordingto another embodiment of the present disclosure. FIG. 3A is a crosssectional view along the X direction (source-drain direction), FIG. 3Bis a cross sectional view corresponding to Y1-Y1 of FIG. 3A, FIG. 3C isa cross sectional view corresponding to Y2-Y2 of FIG. 3A and FIG. 3Dshows a cross sectional view corresponding to Y3-Y3 of FIG. 3A.Material, configuration, dimensions and/or processes the same as orsimilar to the foregoing embodiments described with respect to FIGS.1A-2D may be employed in the embodiment of FIGS. 3A-3D, and detailedexplanation thereof may be omitted.

In the embodiments of FIGS. 3A-3D, the GAA FET shown in FIGS. 1A-1D is ap-type GAA FET.

The semiconductor wires 20, which are channel layers and are made ofSi_(1-x)Ge_(x), where x is equal to or more than about 0.1 and equal toor less than about 0.6 (hereinafter may be merely referred to as SiGe),are disposed over the substrate 10. In some embodiments, thesemiconductor wires 20 are disposed over a fin structure 11 (see, FIG.5) protruding from the substrate 10. The thickness of the semiconductorwires 20 is in a range from about 5 nm to about 15 nm and the width ofthe semiconductor wires 20 is in a range from about 5 nm to about 15 nmin some embodiments. Each of the channel layers 20 is wrapped around bya gate dielectric layer 82 and a gate electrode layer 84. In someembodiments, the gate dielectric layer 82 includes an interfacial layerand a high-k dielectric layer. The gate structure includes the gatedielectric layer 82, the gate electrode layer 84 and sidewall spacers40. Although FIGS. 3A-3C shows four semiconductor wires 20, the numberof the semiconductor wires 20 is not limited to four, and may be assmall as one or more than four and may be up to ten.

Further, a source/drain epitaxial layer 55 is disposed over thesubstrate 10. The source/drain epitaxial layer 55 is in direct contactwith and faces of the channel layers 20, and is separated by insulatinginner spacers 65 and the gate dielectric layer 82 from the gateelectrode layer 84. The source/drain epitaxial layer 55 is made of oneor more of Si, SGe and SiGeB. In some embodiments, an additionalinsulating layer (not shown) is conformally formed on the inner surfaceof the spacer regions.

As shown FIG. 3A, the cross section along the X direction of the innerspacer 65 has a wedge-shape or a substantially triangular shape. In someembodiments, the inner spacers 65 are disposed above the uppermostsemiconductor wire 25.

FIGS. 4A-4D show various views of a p-type GAA FET device according toanother embodiment of the present disclosure. FIG. 4A is a crosssectional view along the X direction (source-drain direction), FIG. 4Bis a cross sectional view corresponding to Y1-Y1 of FIG. 4A, FIG. 4C isa cross sectional view corresponding to Y2-Y2 of FIG. 4A and FIG. 4Dshows a cross sectional view corresponding to Y3-Y3 of FIG. 4A.Material, configuration, dimensions and/or processes the same as orsimilar to the foregoing embodiments described with respect to FIGS.1A-3D may be employed in the embodiment of FIGS. 4A-4D, and detailedexplanation thereof may be omitted.

In this embodiment, the source/drain epitaxial layer 55 wraps around endportions of the semiconductor wires 20 disposed at the source/drainregions, or the semiconductor wires 20 pass through the source/drainepitaxial layer 55.

In some embodiments, two or more of the GAA FETs shown in FIGS. 1A-4Dare disposed on one semiconductor substrate (chip) to achieve variouscircuit functions.

FIGS. 5A to 20B show various stages of manufacturing a semiconductor FETdevice according to an embodiment of the present disclosure. In FIGS.7A-20B, the “A” figures are a cross sectional view along the X direction(source-drain direction) for an n-type GAA FET, and the “B” figures area cross sectional view along the X direction for a p-type GAA FET. It isunderstood that in FIGS. 7A-20B, the n-type GAA FET and the p-type GAAFET are formed on the same substrate (a chip) in some embodiments. It isunderstood that additional operations can be provided before, during,and after processes shown by FIGS. 5A-20B, and some of the operationsdescribed below can be replaced or eliminated, for additionalembodiments of the method. The order of the operations/processes may beinterchangeable. Material, configuration, dimensions and/or processesthe same as or similar to the foregoing embodiments described withrespect to FIGS. 1A-4D may be employed in the embodiment of FIGS.5A-20B, and detailed explanation thereof may be omitted.

As shown in FIGS. 5A and 5B, fin structures 29, in which firstsemiconductor layers 20 and second semiconductor layers 25 arealternately stacked, are formed over the substrate 10. The finstructures 29 protrude from an isolation insulating layer 15. The finstructures 29 can be formed by the following operations.

Stacked semiconductor layers are formed over the substrate 10. Thestacked semiconductor layers include the first semiconductor layers 20and the second semiconductor layers 25. The first semiconductor layers20 and the second semiconductor layers 25 are made of materials havingdifferent lattice constants, and may include one or more layers of Si,Ge, SiGe, GaAs, InSb, GaP, GaSb, InAlAs, InGaAs, GaSbP, GaAsSb or InP.

In some embodiments, the first semiconductor layers 20 and the secondsemiconductor layers 25 are made of Si, a Si compound, SiGe, Ge or a Gecompound. In one embodiment, the first semiconductor layers 20 areSi_(1-x)Ge_(x), where x is equal to or more than about 0.1 and equal toor less than about 0.6, and the second semiconductor layers 25 are Si orSi_(1-y)Ge_(y), where y is equal to or less than about 0.2. In thisdisclosure, an “M” compound” or an “M based compound” means the majorityof the compound is M.

The first semiconductor layers 20 and the second semiconductor layers 25are epitaxially formed over the substrate 10. The thickness of the firstsemiconductor layers 20 may be equal to or greater than that of thesecond semiconductor layers 25, and is in a range from about 2 nm toabout 20 nm in some embodiments, and is in a range from about 5 nm toabout 15 nm in other embodiments. The thickness of the secondsemiconductor layers 25 is in a range from about 2 nm to about 20 nm insome embodiments, and is in a range from about 5 nm to about 15 nm inother embodiments. The thickness of each of the first semiconductorlayers 20 may be the same, or may vary.

In some embodiments, the bottom first semiconductor layer (the closestlayer to the substrate 10) is thicker than the remaining firstsemiconductor layers. The thickness of the bottom first semiconductorlayer is in a range from about 10 nm to about 50 nm in some embodiments,or is in a range from 20 nm to 40 nm in other embodiments.

In some embodiments, a mask layer including a first mask layer and asecond mask layer is formed over the stacked layers. The first masklayer is a pad oxide layer made of a silicon oxide, which can be formedby a thermal oxidation. The second mask layer is made of a siliconnitride, which is formed by chemical vapor deposition (CVD), includinglow pressure CVD (LPCVD) and plasma enhanced CVD (PECVD), physical vapordeposition (PVD), atomic layer deposition (ALD), or other suitableprocess. The mask layer is patterned into a mask pattern by usingpatterning operations including photo-lithography and etching.

Next, the stacked layers of the first and second semiconductor layers20, 25 are patterned by using the patterned mask layer, thereby thestacked layers are formed into fin structures 29 extending in the Xdirection, as shown in FIGS. 5A and 5B. In FIG. 5B, two fin structures29 are arranged in the Y direction. But the number of the fin structuresis not limited to two, and may be as small as one and three or more. Insome embodiments, one or more dummy fin structures are formed on bothsides of the fin structures 29 to improve pattern fidelity in thepatterning operations. As shown in FIG. 5B, the fin structures 29 haveupper portions constituted by the stacked semiconductor layers 20, 25and well portions 11.

The width of the upper portion of the fin structure 29 along the Ydirection is in a range from about 10 nm to about 40 nm in someembodiments, and is in a range from about 20 nm to about 30 nm in otherembodiments.

The stacked fin structure 29 may be patterned by any suitable method.For example, the structures may be patterned using one or morephotolithography processes, including double-patterning ormulti-patterning processes. Generally, double-patterning ormulti-patterning processes combine photolithography and self-alignedprocesses, allowing patterns to be created that have, for example,pitches smaller than what is otherwise obtainable using a single, directphotolithography process. For example, in one embodiment, a sacrificiallayer is formed over a substrate and patterned using a photolithographyprocess. Spacers are formed alongside the patterned sacrificial layerusing a self-aligned process. The sacrificial layer is then removed, andthe remaining spacers may then be used to pattern the stacked finstructure 29.

After the fin structures 29 are formed, an insulating material layerincluding one or more layers of insulating material is formed over thesubstrate so that the fin structures are fully embedded in theinsulating layer. The insulating material for the insulating layer mayinclude silicon oxide, silicon nitride, silicon oxynitride (SiON),SiOCN, SiCN, fluorine-doped silicate glass (FSG), or a low-k dielectricmaterial, formed by LPCVD (low pressure chemical vapor deposition),plasma-CVD or flowable CVD. An anneal operation may be performed afterthe formation of the insulating layer. Then, a planarization operation,such as a chemical mechanical polishing (CMP) method and/or an etch-backmethod, is performed such that the upper surface of the uppermost secondsemiconductor layer 25 is exposed from the insulating material layer. Insome embodiments, one of more fin liner layers 16 (see, FIG. 8C) areformed over the fin structures before forming the insulating materiallayer. In some embodiments, the fin liner layers include a first finliner layer formed over the substrate 10 and sidewalls of the bottompart of the fin structures 11, and a second fin liner layer formed onthe first fin liner layer. The fin liner layers are made of siliconnitride or a silicon nitride-based material (e.g., SiON, SiCN or SiOCN).The fin liner layers may be deposited through one or more processes suchas physical vapor deposition (PVD), chemical vapor deposition (CVD), oratomic layer deposition (ALD), although any acceptable process may beutilized.

Then, as shown in FIG. 5B, the insulating material layer is recessed toform an isolation insulating layer 15 so that the upper portions of thefin structures 29 are exposed. With this operation, the fin structures29 are separated from each other by the isolation insulating layer 15,which is also called a shallow trench isolation (STI). The isolationinsulating layer 15 may be made of suitable dielectric materials such assilicon oxide, silicon nitride, silicon oxynitride, fluorine-dopedsilicate glass (FSG), low-k dielectrics such as carbon doped oxides,extremely low-k dielectrics such as porous carbon doped silicon dioxide,a polymer such as polyimide, combinations of these, or the like. In someembodiments, the isolation insulating layer 15 is formed through aprocess such as CVD, flowable CVD (FCVD), or a spin-on-glass process,although any acceptable process may be utilized.

In some embodiments, the insulating material layer 15 is recessed untilthe upper portion of the fin structure (well layer) 11 is exposed. Inother embodiments, the upper portion of the fin structure 11 is notexposed. The first semiconductor layers 20 are sacrificial layers whichare subsequently partially removed, and the second semiconductor layers25 are subsequently formed into semiconductor wires as channel layers ofan n-type GAA FET. For a p-type GAA FET, the second semiconductor layers25 are sacrificial layers which are subsequently partially removed, andthe first semiconductor layers 20 are subsequently formed intosemiconductor wires as channel layers.

After the isolation insulating layer 15 is formed, a sacrificial (dummy)gate structure 49 is formed, as shown in FIGS. 6A and 6B. FIGS. 6A and6B illustrates a structure after a sacrificial gate structure 49 isformed over the exposed fin structures 29. The sacrificial gatestructure 49 is formed over a portion of the fin structures which is tobe a channel region. The sacrificial gate structure 49 defines thechannel region of the GAA FET. The sacrificial gate structure 49includes a sacrificial gate dielectric layer 41 and a sacrificial gateelectrode layer 42. The sacrificial gate dielectric layer 41 includesone or more layers of insulating material, such as a silicon oxide-basedmaterial. In one embodiment, silicon oxide formed by CVD is used. Thethickness of the sacrificial gate dielectric layer 41 is in a range fromabout 1 nm to about 5 nm in some embodiments.

The sacrificial gate structure 49 is formed by first blanket depositingthe sacrificial gate dielectric layer 41 over the fin structures. Asacrificial gate electrode layer is then blanket deposited on thesacrificial gate dielectric layer and over the fin structures, such thatthe fin structures are fully embedded in the sacrificial gate electrodelayer. The sacrificial gate electrode layer includes silicon such aspolycrystalline silicon or amorphous silicon. The thickness of thesacrificial gate electrode layer is in a range from about 100 nm toabout 200 nm in some embodiments. In some embodiments, the sacrificialgate electrode layer is subjected to a planarization operation. Thesacrificial gate dielectric layer and the sacrificial gate electrodelayer are deposited using CVD, including LPCVD and PECVD, PVD, ALD, orother suitable process. Subsequently, a mask layer is formed over thesacrificial gate electrode layer. The mask layer includes a pad siliconnitride layer 43 and a silicon oxide mask layer 44.

Next, a patterning operation is performed on the mask layer andsacrificial gate electrode layer is patterned into the sacrificial gatestructure 49, as shown in FIGS. 6A and 6B. The sacrificial gatestructure includes the sacrificial gate dielectric layer 41, thesacrificial gate electrode layer 42 (e.g., poly silicon), the padsilicon nitride layer 43 and the silicon oxide mask layer 44. Bypatterning the sacrificial gate structure, the stacked layers of thefirst and second semiconductor layers are partially exposed on oppositesides of the sacrificial gate structure, thereby defining source/drainregions, as shown in FIGS. 6A and 6B. In this disclosure, a source and adrain are interchangeably used and the structures thereof aresubstantially the same. In FIGS. 6A and 6B, one sacrificial gatestructure is formed over two fin structures, but the number of thesacrificial gate structures is not limited to one. Two or moresacrificial gate structures are arranged in the X direction in someembodiments. In certain embodiments, one or more dummy sacrificial gatestructures are formed on both sides of the sacrificial gate structuresto improve pattern fidelity.

Further, a first cover layer 45 for sidewall spacers is formed over thesacrificial gate structure 49, as shown in FIGS. 6A and 6B. The firstcover layer 45 is deposited in a conformal manner so that it is formedto have substantially equal thicknesses on vertical surfaces, such asthe sidewalls, horizontal surfaces, and the top of the sacrificial gatestructure, respectively. In some embodiments, the first cover layer 45has a thickness in a range from about 5 nm to about 20 nm. The firstcover layer 45 includes one or more of silicon nitride, SiON, SiCN,SiCO, SiOCN or any other suitable dielectric material. The cover layer45 can be formed by ALD or CVD, or any other suitable method.

FIG. 7A shows a cross sectional view along the X direction in an n-typeregion, and FIG. 7B shows a cross sectional view along the X directionin a p-type region. Next, as shown in FIGS. 7A and 7B, in the n-typeregion, the first cover layer 45 is anisotropicly etched to remove thefirst cover layer 45 disposed on the source/drain region, while leavingthe first cover layer 45 as sidewall spacers on side faces of thesacrificial gate structure 49. Then the stacked structure of the firstsemiconductor layers 20 and the second semiconductor layer 25 is etcheddown at the source/drain region, by using one or more lithography andetching operations, thereby forming a source/drain space 21. In someembodiments, the substrate 10 (or the bottom part of the fin structures11) is also partially etched. The p-type region is covered by aprotective layer 101, such a photo resist layer, as shown in FIG. 7B.

Further, as shown in FIGS. 8A-8C, the first semiconductor layers 20 arelaterally etched in the X direction within the source/drain space 21,thereby forming cavities 22. The amount of etching of the firstsemiconductor layer 20 is in a range from about 2 nm to about 10 nm insome embodiments. When the first semiconductor layers 20 are Ge or SiGeand the second semiconductor layers 25 are Si, the first semiconductorlayers 20 can be selectively etched by using a wet etchant such as, butnot limited to, an HCl solution. By using the HCl acid solution and byselecting an appropriate crystal orientation of the first semiconductorlayers 20, the etched surface of the end faces of the firstsemiconductor layers 20 have a V-shape (90 degree rotated) or asubstantially triangular shape, defined by (111) facets of the firstsemiconductor layers 20. In other embodiments, a mixed solution ofNH₄OH, H₂O₂ and H₂O is used to selectively etch the first semiconductorlayer 20 to obtain the etched surface of the end faces of the firstsemiconductor layers 20 having a V-shape (90 degree rotated) or asubstantially triangular shape, defined by (111) facets of the firstsemiconductor layers 20. The mixed solution is used at a temperature ina range from about 60° C. to about 90° C. in some embodiments. After thelateral etching, the protective layer 101 in the p-type region isremoved.

As shown in FIG. 9A, a first insulating layer 30 is conformally formedon the etched lateral ends of the first semiconductor layers 20 and onend faces of the second semiconductor layers 25 in the source/drainspace 21 and over the sacrificial gate structure. The first insulatinglayer 30 includes one of silicon nitride and silicon oxide, SiON, SiOC,SiCN and SiOCN, or any other suitable dielectric material. The firstinsulating layer 30 is made of a different material than the sidewallspacers (first cover layer) 45. The first insulating layer 30 has athickness in a range from about 1.0 nm to about 10.0 nm. In otherembodiments, the first insulating layer 30 has a thickness in a rangefrom about 2.0 nm to about 5.0 nm. The first insulating layer 30 can beformed by ALD or any other suitable methods. By conformally forming thefirst insulating layer 30, the cavities 22 are fully filled with thefirst insulating layer 30. In the p-type region, the first insulatinglayer 30 is formed on the first cover layer 45, as shown in FIG. 9B.

After the first insulating layer 30 is formed, an etching operation isperformed to partially remove the first insulating layer 30, therebyforming inner spacers 35, as shown in FIG. 10A. In some embodiments, thep-type region is covered by a protective layer 103, for example, a photoresist pattern, as shown in FIG. 10B. In other embodiments, theprotective layer 103 is not used, and in such a case, the firstinsulating layer 30 in the p-type region is simultaneously removedduring the etching operation performed in the n-type region.

In some embodiments, before forming the first insulating layer 30, anadditional insulating layer having a smaller thickness than the firstinsulating layer 30 is formed, and thus the inner spacers 35 have atwo-layer structure.

Subsequently, as shown in FIG. 11A, a source/drain epitaxial layer 50 isformed in the source/drain space 21, in the n-type region. Thesource/drain epitaxial layer 50 includes one or more layers of Si, SiP,SiC and SiCP for an n-channel FET. The source/drain epitaxial layer 50is formed by an epitaxial growth method using CVD, ALD or molecular beamepitaxy (MBE). As shown in FIGS. 11A and 11B, the source/drain epitaxiallayer 50 is selectively formed on semiconductor regions. Thesource/drain epitaxial layer 50 is formed in contact with end faces ofthe second semiconductor layers 25, and formed in contact with the innerspacers 35.

Then, as shown in FIGS. 12A and 12B, a second cover layer 47 is formedboth in the n-type region and the p-type region. The second cover layer47 includes one of silicon nitride and silicon oxide, SiON, SiOC, SiCNand SiOCN, or any other suitable dielectric material. The second coverlayer 47 is made of a different material than the sidewall spacers(first cover layer) 45. The second insulating layer 47 can be formed byALD or any other suitable methods.

Next, as shown in FIGS. 13A and 13B, while the n-type region is coveredby a protective layer 111, for example, a photo resist pattern, thesecond cover layer 47 is removed from the p-type region. Further, thefirst cover layer 45 is anisotropicaly etched to remove the first coverlayer 45 disposed on the source/drain region, while leaving the firstcover layer 45 as sidewall spacers on side faces of the sacrificial gatestructure 49 in the p-type region.

Further, as shown in FIG. 14B, the second semiconductor layer 25 in thesource/drain region of the fin structure, which is not covered by thesacrificial gate structure, is etched, thereby leaving the firstsemiconductor layers 20 remaining in the source/drain region. The n-typeregion is covered by the protective layer 111 in some embodiments, asshown in FIG. 14A. In other embodiments, the protective layer 111 isremoved before etching the source/drain region in the p-type region, andthe second cover layer 47 protects the n-type region.

In addition, the second semiconductor layers 25 are laterally etched inthe X direction within the source/drain space 51, thereby formingcavities 52, as shown in FIG. 15B. The amount of etching of the secondsemiconductor layer 25 is in a range from about 2 nm to about 10 nm insome embodiments. When the first semiconductor layers 20 are Ge or SiGeand the second semiconductor layers 25 are Si, the second semiconductorlayers 25 can be selectively etched by using a wet etchant such as, butnot limited to, an ammonium hydroxide (NH₄OH) solution and/or atetramethylammonium hydroxide (TMAH) solution. By using the ammoniumhydroxide (NH₄OH) solution and/or the tetramethylammonium hydroxide(TMAH) solution and by selecting an appropriate crystal orientation ofthe second semiconductor layers 25, the etched surface of the end facesof the second semiconductor layers 25 have a V-shape (90 degree rotated)or a substantially triangular shape, defined by (111) facets of thesecond semiconductor layers 25. After the lateral etching, theprotective layer 111, if remaining at this stage, in the p-type regionis removed.

Then, as shown in FIGS. 16A and 16B, a second insulating layer 60 isformed over both the p-type region and the n-type region. In someembodiments, the second insulating layer 60 fully fills the source/drainspace 51 between the adjacent first semiconductor layers 20. The secondinsulating layer 60 includes one of silicon nitride and silicon oxide,SiON, SiOC, SiCN and SiOCN, or any other suitable dielectric material.The second insulating layer 60 is made of a different material than thesidewall spacers (first cover layer) 45. The second insulating layer 60has a thickness in a range from about 1.0 nm to about 10.0 nm. In otherembodiments, the second insulating layer 60 has a thickness in a rangefrom about 2.0 nm to about 5.0 nm. The second insulating layer 60 can beformed by ALD or any other suitable methods. By forming the secondinsulating layer 60, the cavity 52 is fully filled with the secondinsulating layer 60. In the n-type region, the second insulating layer60 is formed on the second cover layer 47, as shown in FIG. 16B.

After the second insulating layer 60 is formed, an etching operation isperformed to partially remove the second insulating layer 60, therebyforming inner spacers 65, as shown in FIG. 17B, while the n-type regionis covered by the second cover layer 47, as shown in FIG. 17A. In someembodiments, before forming the second insulating layer 60, anadditional insulating layer having a smaller thickness than the secondinsulating layer 60 is formed, and thus the inner spacers 65 has atwo-layer structure.

Subsequently, as shown in FIGS. 18A and 18B, a source/drain epitaxiallayer 55 is formed in the source/drain space 51, in the p-type region.The source/drain epitaxial layer 55 includes one or more layers of Si,SiGe and Ge for a p-channel FET. For the P-channel FET, boron (B) mayalso be contained in the source/drain. The source/drain epitaxial layer55 is formed by an epitaxial growth method using CVD, ALD or molecularbeam epitaxy (MBE). The source/drain epitaxial layer 55 is formed towrap around end portions of the first semiconductor layers 20, andformed in contact with the inner spacers 65. In some embodiments, thefirst semiconductor layers 20 pass through the source/drain epitaxiallayer 55. After the source/drain epitaxial layer 55 is selectivelyformed on semiconductor regions in the p-type region, the second coverlayer 47 in the n-type region is removed, as shown in FIG. 18A.

Subsequently, an interlayer dielectric (ILD) layer 70 is formed over thesource/drain epitaxial layers 50 and 55. The materials for the ILD layer70 include compounds comprising Si, O, C and/or H, such as siliconoxide, SiCOH and SiOC. Organic materials, such as polymers, may be usedfor the ILD layer 70. After the ILD layer 70 is formed, a planarizationoperation, such as CMP, is performed, so that the top portion of thesacrificial gate electrode layer 42 is exposed.

Then, the sacrificial gate electrode layer 42 and sacrificial gatedielectric layer 41 are removed. The ILD layer 70 protects thesource/drain epitaxial layers 50 and 55 during the removal of thesacrificial gate structures. The sacrificial gate structures can beremoved using plasma dry etching and/or wet etching. When thesacrificial gate electrode layer 42 is polysilicon and the ILD layer 70is silicon oxide, a wet etchant such as a TMAH solution can be used toselectively remove the sacrificial gate electrode layer 42. Thesacrificial gate dielectric layer 41 is thereafter removed using plasmadry etching and/or wet etching.

After the sacrificial gate structures are removed, the firstsemiconductor layers 20 are removed in the n-type region, therebyforming wires (channel regions) of the second semiconductor layers 25,as shown in FIG. 19A. The first semiconductor layers 20 can be removedor etched using an etchant that can selectively etch the firstsemiconductor layers 20 against the second semiconductor layers 25, asset forth above. As shown in FIG. 19A, since the first insulating layers(inner spacers) 35 are formed, the etching of the first semiconductorlayers 20 stops at the first insulating layer 35. In other words, thefirst insulating layer 35 functions as an etch-stop layer for etching ofthe first semiconductor layers 20. The channel formation operations forthe n-type region are performed, while the p-type region is covered by aprotective layer.

Similarly, the second semiconductor layers 25 are removed in the p-typeregion, thereby forming wires (channel regions) of the firstsemiconductor layers 20, as shown in FIG. 19B. The second semiconductorlayers 25 can be removed or etched using an etchant that can selectivelyetch the second semiconductor layers 25 against the first semiconductorlayers 20, as set forth above. As shown in FIG. 19B, since the secondinsulating layers (inner spacers) 65 are formed, the etching of thesecond semiconductor layers 25 stops at the second insulating layer 65.In other words, the second insulating layer 65 functions as an etch-stoplayer for etching of the second semiconductor layers 25. The channelformation operations for the p-type region are performed, while then-type region is covered by a protective layer. The formation of thechannel regions for the p-type region can be performed after theformation of the channel regions for the n-type region.

After the semiconductor wires (channel regions) of the secondsemiconductor layers 25 in the n-type region and the first semiconductorlayers 20 in the p-type region are formed, a gate dielectric layer 82 isformed around each channel regions for the n-type region and the p-typeregion. Further, a gate electrode layer 84 is formed on the gatedielectric layer 82, as shown in FIGS. 20A and 20B. In some embodiments,the structure and/or material of the gate electrode for the n-type GAAFET are different from the structure and/or material of the gateelectrode for the p-type GAA FET.

In certain embodiments, the gate dielectric layer 82 includes one ormore layers of a dielectric material, such as silicon oxide, siliconnitride, or high-k dielectric material, other suitable dielectricmaterial, and/or combinations thereof. Examples of high-k dielectricmaterial include HfO₂, HfSiO, HfSiON, HfTaO, HfTiO, HfZrO, zirconiumoxide, aluminum oxide, titanium oxide, hafnium dioxide-alumina(HfO₂—Al₂O₃) alloy, other suitable high-k dielectric materials, and/orcombinations thereof. In some embodiments, the gate dielectric layer 82includes an interfacial layer (not shown) formed between the channellayers and the dielectric material.

The gate dielectric layer 82 may be formed by CVD, ALD or any suitablemethod. In one embodiment, the gate dielectric layer 82 is formed usinga highly conformal deposition process such as ALD in order to ensure theformation of a gate dielectric layer having a uniform thickness aroundeach channel layers. The thickness of the gate dielectric layer 82 is ina range from about 1 nm to about 6 nm in one embodiment.

The gate electrode layer 84 is formed on the gate dielectric layer 82 tosurround each channel layer. The gate electrode 84 includes one or morelayers of conductive material, such as polysilicon, aluminum, copper,titanium, tantalum, tungsten, cobalt, molybdenum, tantalum nitride,nickel silicide, cobalt silicide, TiN, WN, TiAl, TiAlN, TaCN, TaC,TaSiN, metal alloys, other suitable materials, and/or combinationsthereof.

The gate electrode layer 84 may be formed by CVD, ALD, electro-plating,or other suitable method. The gate electrode layer is also depositedover the upper surface of the ILD layer 70. The gate dielectric layerand the gate electrode layer formed over the ILD layer 70 are thenplanarized by using, for example, CMP, until the top surface of the ILDlayer 70 is revealed. In some embodiments, after the planarizationoperation, the gate electrode layer 84 is recessed and a cap insulatinglayer (not shown) is formed over the recessed gate electrode 84. The capinsulating layer includes one or more layers of a silicon nitride-basedmaterial, such as silicon nitride. The cap insulating layer can beformed by depositing an insulating material followed by a planarizationoperation.

In certain embodiments of the present disclosure, one or more workfunction adjustment layers (not shown) are interposed between the gatedielectric layer 82 and the gate electrode 84. The work functionadjustment layers are made of a conductive material such as a singlelayer of TiN, TaN, TaAlC, TiC, TaC, Co, Al, TiAl, HfTi, TiSi, TaSi orTiAlC, or a multilayer of two or more of these materials. For then-channel FET, one or more of TaN, TaAlC, TiN, TiC, Co, TiAl, HfTi, TiSiand TaSi is used as the work function adjustment layer, and for thep-channel FET, one or more of TiAlC, Al, TiAl, TaN, TaAlC, TiN, TiC andCo is used as the work function adjustment layer. The work functionadjustment layer may be formed by ALD, PVD, CVD, e-beam evaporation, orother suitable process. Further, the work function adjustment layer maybe formed separately for the n-channel FET and the p-channel FET whichmay use different metal layers.

Subsequently, contact holes are formed in the ILD layer 70 by using dryetching, thereby exposing the upper portion of the source/drainepitaxial layer 50. In some embodiments, a silicide layer is formed overthe source/drain epitaxial layer 50. The silicide layer includes one ormore of WSi, CoSi, NiSi, TiSi, MoSi and TaSi. Then, a conductive contactlayer 72 is formed in the contact holes as shown in FIGS. 1A-1D. Theconductive contact layer 72 includes one or more of Co, Ni, W, Ti, Ta,Cu, Al, TiN and TaN. Further, a conductive contact plug 75 is formed onthe conductive contact layer 72. The conductive contact plug 75 includesone or more layers of Co, Ni, W, Ti, Ta, Cu, Al, TiN and TaN.

It is noted that in the foregoing embodiments, the order of theprocesses for the n-type GAA FET and the processes for the p-type GAAFET can be interchangeable. For example, in the foregoing embodiments,the inner spacers 35 for the n-type GAA FET are first formed and thenthe inner spacers 65 for the p-type GAA FET are formed. In otherembodiments, the inner spacers 65 for the p-type GAA FET are firstformed and then the inner spacers 35 for the n-type GAA FET are formed.

It is understood that the GAA FETs undergo further CMOS processes toform various features such as contacts/vias, interconnect metal layers,dielectric layers, passivation layers, etc.

FIGS. 21A-32B show various stages of manufacturing a semiconductor FETdevice according to another embodiment of the present disclosure. InFIGS. 21A-32B, the “A” figures are a cross sectional view along the Xdirection (source-drain direction) for an n-type GAA FET, and the “B”figures are a cross sectional view along the X direction for a p-typeGAA FET. It is understood that in FIGS. 21A-32B, the n-type GAA FET andthe p-type GAA FET are formed on the same substrate (a chip) in someembodiments. It is understood that additional operations can be providedbefore, during, and after processes shown by FIGS. 21A-32B, and some ofthe operations described below can be replaced or eliminated, foradditional embodiments of the method. The order of theoperations/processes may be interchangeable. Material, configuration,dimensions and/or processes the same as or similar to the foregoingembodiments described with respect to FIGS. 1A-20B may be employed inthe embodiment of FIGS. 21A-32B, and detailed explanation thereof may beomitted.

After the operations explained with respect to FIGS. 8A and 8B, a secondcover layer 36 is formed both in the n-type region and the p-typeregion, as shown in FIGS. 21A and 21B. The second cover layer 36includes one of silicon nitride and silicon oxide, SiON, SiOC, SiCN andSiOCN, or any other suitable dielectric material. The second cover layer36 is made of a different material than the sidewall spacers (firstcover layer) 45. The second insulating layer 36 can be formed by ALD orany other suitable methods.

Then, the second cover layer 36 in the p-type region is selectivelyremoved by one or more lithography and etching operations. Further, thefirst cover layer 45 is anisotropicaly etched to remove the first coverlayer 45 disposed on the source/drain region, while leaving the firstcover layer 45 as sidewall spacers on side faces of the sacrificial gatestructure 49 in the p-type region.

Further, as shown in FIG. 22B, the first and second semiconductor layers20 and 25 in the source/drain region of the fin structure in the p-typeregion, which is not covered by the sacrificial gate structure 49, isetched, thereby forming a source/drain space 51. The n-type region iscovered by the second cover layer 36, as shown in FIG. 22A.

In addition, the second semiconductor layers 25 are laterally etched inthe X direction within the source/drain space 51, thereby formingcavities 52, as shown in FIG. 23B. The amount of etching of the secondsemiconductor layer 25 is in a range from about 2 nm to about 10 nm insome embodiments. When the first semiconductor layers 20 are Ge or SiGeand the second semiconductor layers 25 are Si, the second semiconductorlayers 25 can be selectively etched by using a wet etchant such as, butnot limited to, an ammonium hydroxide (NH₄OH) solution and/or atetramethylammonium hydroxide (TMAH) solution. By using the ammoniumhydroxide (NH₄OH) solution and/or the tetramethylammonium hydroxide(TMAH) solution and by selecting an appropriate crystal orientation ofthe second semiconductor layers 25, the etched surface of the end facesof the second semiconductor layers 25 have a V-shape (90 degree rotated)or a substantially triangular shape, defined by (111) facets of thesecond semiconductor layers 25. The n-type region is covered by thesecond cover layer 36, as shown in FIG. 23A.

Then, as shown in FIGS. 24A and 24B, the second cover layer 36 isremoved in the n-type region by one or more etching operations. Sincethe second cover layer 36 is made of a different material than thesidewall spacers 45, the second cover layer 36 can be selectivelyremoved.

Then, a first insulating layer 30 is conformally formed on the etchedlateral ends of the first semiconductor layer 20 and on end faces of thesecond semiconductor layer 25 in the source/drain space 21 in the n-typeregion, and on the etched lateral ends of the second semiconductorlayers 25 and on end faces of the first semiconductor layer 20 in thesource/drain space 51 in the p-type region, as shown in FIGS. 25A and25B. The first insulating layer 30 is also formed over the sacrificialgate structure. The first insulating layer 30 includes one of siliconnitride and silicon oxide, SiON, SiOC, SiCN and SiOCN, or any othersuitable dielectric material. The first insulating layer 30 is made of adifferent material than the sidewall spacers (first cover layer) 45. Thefirst insulating layer 30 has a thickness in a range from about 1.0 nmto about 10.0 nm. In other embodiments, the first insulating layer 30has a thickness in a range from about 2.0 nm to about 5.0 nm. The firstinsulating layer 30 can be formed by ALD or any other suitable methods.By conformally forming the first insulating layer 30, the cavities 22and 52 are fully filled with the first insulating layer 30.

After the first insulating layer 30 is formed, an etching operation isperformed to partially remove the first insulating layer 30, therebyforming inner spacers 35 and 65, as shown in FIGS. 26A and 26B.

In some embodiments, before forming the first insulating layer 30, anadditional insulating layer having a smaller thickness than the firstinsulating layer 30 is formed, and thus the inner spacers 35 and 65 havea two-layer structure.

After the inner spacers 35 and 65 are formed, a third cover layer 90 isformed to protect the p-type region, as shown in FIGS. 27A and 27B. Thethird cover layer 90 includes one or more layers of silicon nitride andsilicon oxide, SiON, SiOC, SiCN and SiOCN, or any other suitabledielectric material. In some embodiments, the third cover layer 90includes a under layer 91 made of a silicon oxide based material (e.g.,silicon oxide or SiOC) and an upper layer 92 made of a silicon nitridebased material (e.g., silicon nitride or SiON). The under layer 91 ismade of a different material than the sidewall spacers (first coverlayer) 45. The third cover layer 90 can be formed by ALD or any othersuitable methods.

Subsequently, as shown in FIG. 28A, a source/drain epitaxial layer 50 isformed in the source/drain space 21, in the n-type region. Thesource/drain epitaxial layer 50 includes one or more layers of Si, SiP,SiC and SiCP for an n-channel FET. The source/drain epitaxial layer 50is formed by an epitaxial growth method using CVD, ALD or molecular beamepitaxy (MBE). As shown in FIGS. 28A and 28B, the source/drain epitaxiallayer 50 is selectively formed on semiconductor regions. Thesource/drain epitaxial layer 50 is formed in contact with end faces ofthe second semiconductor layers 25, and formed in contact with the innerspacers 35.

Then, as shown in FIG. 29B, the third cover layer 90 is removed from thep-type region, and a fourth cover layer 94 is formed to protect then-type region, as shown in FIGS. 30A and 30B. The fourth cover layer 94includes one or more layers of silicon nitride and silicon oxide, SiON,SiOC, SiCN and SiOCN, or any other suitable dielectric material. In someembodiments, the fourth cover layer 94 includes a under layer 95 made ofa silicon oxide based material (e.g., SiO₂ or SiOC) and an upper layer96 made of a silicon nitride based material (e.g., silicon nitride orSiON). The under layer 95 is made of a different material than thesidewall spacers (first cover layer) 45. The fourth cover layer 94 canbe formed by ALD or any other suitable methods.

Subsequently, as shown in FIG. 31B, a source/drain epitaxial layer 55 isformed in the source/drain space 51, in the p-type region. Thesource/drain epitaxial layer 55 is made of one or more of Si, SGe andSiGeB. The source/drain epitaxial layer 55 is formed by an epitaxialgrowth method using CVD, ALD or molecular beam epitaxy (MBE). As shownin FIGS. 31A and 31B, the source/drain epitaxial layer 55 is selectivelyformed on semiconductor regions. The source/drain epitaxial layer 55 isformed in contact with end faces of the first semiconductor layers 20,and formed in contact with the inner spacers 65. Then, as shown in FIGS.32A and 32B, the fourth cover layer 94 is removed from the n-typeregion.

Subsequently, the same as or similar operations explained with respectto FIGS. 19A-20B are performed to form the metal gate structure and thecontact structures. It is noted that in the foregoing embodiments, theorder of the processes for the n-type GAA FET and the processes for thep-type GAA FET can be interchangeable. It is understood that the GAAFETs undergo further CMOS processes to form various features such ascontacts/vias, interconnect metal layers, dielectric layers, passivationlayers, etc.

The various embodiments or examples described herein offer severaladvantages over the existing art. For example, in the presentdisclosure, in a GAA FET, an inner spacer having a triangle shape (or awedge-shape) is provided between a metal gate electrode and asource/drain epitaxial layer. Compared with a rectangular shape, thetriangle shape (or a wedge-shape) inner spacers can provide a largereffective gate width (source-drain direction) because more areas of thesemiconductor wires can be wrapped around by the gate dielectric layerand the gate electrode. The methods disclosed herein uniformly form theinner spacers by using wet etching. Further, due to a self-limited etchstop property of the inner spacers, it is possible to more preciselycontrol gate formation processes. With the foregoing embodiments, it ispossible to more precisely control the thickness, the shape and/or thelocation of the inner spacers and thus to control capacitances aroundthe source/drain and the gate.

It will be understood that not all advantages have been necessarilydiscussed herein, no particular advantage is required for allembodiments or examples, and other embodiments or examples may offerdifferent advantages.

In accordance with an aspect of the present disclosure, in a method ofmanufacturing a semiconductor device, a fin structure, in which firstsemiconductor layers and second semiconductor layers are alternatelystacked, is formed. A sacrificial gate structure is formed over the finstructure. A source/drain region of the fin structure, which is notcovered by the sacrificial gate structure, is etched, thereby forming asource/drain space. The first semiconductor layers are laterally etchedthrough the source/drain space. An inner spacer made of a dielectricmaterial is formed on an end of each of the etched first semiconductorlayers. A source/drain epitaxial layer is formed in the source/drainspace to cover the inner spacer. A lateral end of each of the firstsemiconductor layers has a V-shape cross section after the firstsemiconductor layers are laterally etched. In one or more of theforegoing or following embodiments, the lateral end of each of the firstsemiconductor layers has a (111) facet of a semiconductor crystal. Inone or more of the foregoing or following embodiments, the firstsemiconductor layers are laterally etched by wet etching. In one or moreof the foregoing or following embodiments, the wet etching utilizes anHCl acid solution or a mixed solution of NH₄OH, H₂O₂ and H₂O. In one ormore of the foregoing or following embodiments, the inner spacer isformed by the following operations. A dielectric layer is formed in thesource/drain space, and the dielectric layer is etched, thereby leavingthe inner spacer on the end of each of the etched first semiconductorlayers remaining. In one or more of the foregoing or followingembodiments, before the first semiconductors are laterally etched,sidewall spacers are formed on side faces of the sacrificial gatestructure. The sidewall spacers are made of a different material thanthe inner spacer. In one or more of the foregoing or followingembodiments, the inner spacers include at least one of silicon nitrideand silicon oxide. In one or more of the foregoing or followingembodiments, the inner spacers include at least one of SiOC, SiOCN andSiCN. In one or more of the foregoing or following embodiments, in theetching a source/drain region of the fin structure, the first and secondsemiconductor layers of the source/drain region of the fin structure areetched. In one or more of the foregoing or following embodiments, in theetching a source/drain region of the fin structure, the firstsemiconductor layers of the source/drain region of the fin structure areselectively etched, thereby leaving the second semiconductor layersremaining. In one or more of the foregoing or following embodiments,after the source/drain epitaxial layer is formed, the sacrificial gatestructure is removed, thereby exposing a part of the fin structure, thefirst semiconductor layers are removed from the exposed fin structure,thereby forming channel layers including the second semiconductorlayers, and a gate dielectric layer and a gate electrode layer areformed around the channel layers. The gate electrode layer is isolatedfrom the source/drain epitaxial layer by the inner spacer and the gatedielectric layer. In one or more of the foregoing or followingembodiments, the first semiconductor layers are made of SiGe, and thesecond semiconductor layers are made of Si. In one or more of theforegoing or following embodiments, the first semiconductor layers aremade of Si, and the second semiconductor layers are made of SiGe.

In accordance with another aspect of the present disclosure, in a methodof manufacturing a semiconductor device, a first fin structure and asecond fin structure, in both which first semiconductor layers andsecond semiconductor layers are alternately stacked, are formed. A firstsacrificial gate structure is formed over the first fin structure and asecond sacrificial gate structure over the second fin structure. Whilethe second fin structure with the second sacrificial gate structure areprotected, a source/drain region of the first fin structure, which isnot covered by the first sacrificial gate structure, is etched therebyforming a first source/drain space, the first semiconductor layers areetched in the first source/drain space, a first inner spacer made of adielectric material is formed on an end of each of the etched firstsemiconductor layers, and a first source/drain epitaxial layer is formedin the first source/drain space to cover the inner spacer, therebyforming a first structure. While the first structure is protected, thesecond semiconductor layers are etched in a source/drain region of thesecond fin structure, which is not covered by the second sacrificialgate structure, thereby forming a second source/drain space, the secondsemiconductor layers are laterally etched through the secondsource/drain space, a second inner spacer made of a dielectric materialis formed on an end of each of the etched second semiconductor layers,and a second source/drain epitaxial layer is formed in the secondsource/drain space to cover the second inner spacer, thereby forming asecond structure. A lateral end of each of the first semiconductorlayers has a V-shape cross section after the first semiconductor layersare laterally etched, and a lateral end of each of the secondsemiconductor layers has a V-shape cross section after the secondsemiconductor layers are laterally etched. In one or more of theforegoing or following embodiments, in the etching the secondsemiconductor layers in a source/drain region of the second finstructure, the second semiconductor layers are selectively etched,thereby leaving the first semiconductor layers remaining, and the secondsource/drain epitaxial layer wraps around the first semiconductorlayers. In one or more of the foregoing or following embodiments, thelateral end of each of the first semiconductor layers and the lateralend of each of the second semiconductor layers have a (111) facet of asemiconductor crystal, respectively. In one or more of the foregoing orfollowing embodiments, the first semiconductor layers are laterallyetched by wet etching utilizing an HCl acid solution or a mixed solutionof NH₄OH, H₂O₂ and H₂O. In one or more of the foregoing or followingembodiments, the second semiconductor layers are laterally etched by wetetching utilizing at least one of an ammonium hydroxide (NH₄OH) solutionand tetramethylammonium hydroxide (TMAH) solution. In one or more of theforegoing or following embodiments, sidewall spacers are formed on sidefaces of the first sacrificial gate structure and on side faces of thesecond sacrificial gate structure. The sidewall spacers are made of adifferent material than the first and second inner spacers.

In accordance with another aspect of the present disclosure, in a methodof manufacturing a semiconductor device, a first fin structure and asecond fin structure, in both which first semiconductor layers andsecond semiconductor layers are alternately stacked, are formed. A firstsacrificial gate structure is formed over the first fin structure and asecond sacrificial gate structure over the second fin structure. Asource/drain region of the first fin structure, which is not covered bythe first sacrificial gate structure, is etched thereby forming a firstsource/drain space, and the first semiconductor layers are laterallyetched in the first source/drain space. A source/drain region of thesecond fin structure, which is not covered by the second sacrificialgate structure, is etched thereby forming a second source/drain space.The second semiconductor layers are laterally etched in the secondsource/drain space. A dielectric layer is formed in the first and secondspaces. A first inner spacer is formed on an end of each of the etchedfirst semiconductor layers and a second inner spacer is formed on an endof each of the etched second semiconductor layers. A first source/drainepitaxial layer is formed in the first source/drain space to cover thefirst inner spacer, and a second source/drain epitaxial layer is formedin the second source/drain space to cover the second inner spacer. Alateral end of each of the first semiconductor layers has a V-shapecross section after the first semiconductor layers are laterally etched,and a lateral end of each of the second semiconductor layers has aV-shape cross section after the second semiconductor layers arelaterally etched.

In accordance with one aspect of the present disclosure, a semiconductordevice includes semiconductor wires disposed over a substrate, asource/drain epitaxial layer in contact with the semiconductor wires, agate dielectric layer disposed on and wrapping around each channelregion of the semiconductor wires, a gate electrode layer disposed onthe gate dielectric layer and wrapping around the each channel region,and insulating spacers disposed in spaces, respectively. The spaces aredefined by adjacent semiconductor wires, the gate electrode layer andthe source/drain region. Each of the insulating spacers has a triangularor wedge-shaped cross section. In one or more of the foregoing orfollowing embodiments, the insulating spacers are in contact with thesource/drain epitaxial layer. In one or more of the foregoing orfollowing embodiments, the semiconductor device further includessidewall spacers disposed on side faces of the gate electrode layer. Thesidewall spacers are made of a different material than the insulatingspacers. In one or more of the foregoing or following embodiments, theinsulating spacers include at least one of silicon nitride and siliconoxide. In one or more of the foregoing or following embodiments, theinsulating spacers include at least one of SiOC, SiOCN and SiCN. In oneor more of the foregoing or following embodiments, the source/drainepitaxial layer is in contact with lateral end faces of thesemiconductor wires. In one or more of the foregoing or followingembodiments, the semiconductor wires are made of Si. In one or more ofthe foregoing or following embodiments, the semiconductor wires are madeof SiGe. In one or more of the foregoing or following embodiments, thesource/drain epitaxial layer wraps around end portions of thesemiconductor wires. In one or more of the foregoing or followingembodiments, the semiconductor wires are made of SiGe.

In accordance with another aspect of the present disclosure, asemiconductor device includes semiconductor wires disposed over asubstrate, a source/drain epitaxial layer in contact with thesemiconductor wires, a gate dielectric layer disposed on and wrappingaround each channel region of the semiconductor wires, a gate electrodelayer disposed on the gate dielectric layer and wrapping around the eachchannel region, and insulating spacers disposed in spaces, respectively.The spaces are defined by adjacent semiconductor wires, the gateelectrode layer and the source/drain region. In one or more of theforegoing or following embodiments, each of the insulating spacers has atriangular or wedge-shaped cross section, and at least one of theinsulating spacers is disposed above an uppermost one of thesemiconductor wires. In one or more of the foregoing or followingembodiments, the semiconductor wires are made of SiGe. In one or more ofthe foregoing or following embodiments, the semiconductor device furtherincludes sidewall spacers disposed on side faces of the gate electrodelayer. The sidewall spacers are made of a different material than theinsulating spacers. In one or more of the foregoing or followingembodiments, the insulating spacers include at least one of siliconnitride and silicon oxide. In one or more of the foregoing or followingembodiments, the insulating spacers include at least one of SiOC, SiOCNand SiCN. In one or more of the foregoing or following embodiments, thesource/drain epitaxial layer is in contact with lateral end faces of thesemiconductor wires.

In accordance with another aspect of the present disclosure, asemiconductor device includes semiconductor wires disposed over asubstrate, a source/drain epitaxial layer in contact with thesemiconductor wires, a gate dielectric layer disposed on and wrappingaround each channel region of the semiconductor wires, a gate electrodelayer disposed on the gate dielectric layer and wrapping around the eachchannel region, and insulating spacers disposed in spaces, respectively,the spaces being defined by adjacent semiconductor wires, the gateelectrode layer and the source/drain region. Each of the insulatingspacers has a triangular or wedge-shaped cross section, and thesource/drain epitaxial layer wraps around end portions of thesemiconductor wires. In one or more of the foregoing or followingembodiments, the semiconductor wires are made of SiGe. In one or more ofthe foregoing or following embodiments, the insulating spacers are incontact with the source/drain epitaxial layer. In one or more of theforegoing or following embodiments, the insulating spacers include atleast one of SiOC, SiOCN and SiCN.

The foregoing outlines features of several embodiments or examples sothat those skilled in the art may better understand the aspects of thepresent disclosure. Those skilled in the art should appreciate that theymay readily use the present disclosure as a basis for designing ormodifying other processes and structures for carrying out the samepurposes and/or achieving the same advantages of the embodiments orexamples introduced herein. Those skilled in the art should also realizethat such equivalent constructions do not depart from the spirit andscope of the present disclosure, and that they may make various changes,substitutions, and alterations herein without departing from the spiritand scope of the present disclosure.

1. A method of manufacturing a semiconductor device, comprising: forminga fin structure in which first semiconductor layers and secondsemiconductor layers are alternately stacked over a bottom finstructure; forming a sacrificial gate structure over the fin structure;etching a source/drain region of the fin structure, which is not coveredby the sacrificial gate structure, thereby forming a source/drain space;laterally etching the first semiconductor layers through thesource/drain space; forming an inner spacer made of a dielectricmaterial on an end of each of the etched first semiconductor layers; andforming a source/drain epitaxial layer in the source/drain space tocover the inner spacer and to fully fill the source/drain space to be incontact with the bottom fin structure, wherein a lateral end of each ofthe first semiconductor layers has a V-shape cross section after thefirst semiconductor layers are laterally etched.
 2. The method of claim1, wherein the lateral end of each of the first semiconductor layers hasa (111) facet of a semiconductor crystal.
 3. The method of claim 1,wherein the first semiconductor layers are laterally etched by wetetching.
 4. The method of claim 3, wherein the wet etching utilizes anHCl acid solution.
 5. The method of claim 1, wherein the inner spacer isformed by: forming a dielectric layer in the source/drain space; andetching the dielectric layer, thereby leaving the inner spacer on theend of each of the etched first semiconductor layers remaining.
 6. Themethod of claim 1, further comprising, before the first semiconductorsare laterally etched forming sidewall spacers on side faces of thesacrificial gate structure, wherein sidewall spacers are made of adifferent material than the inner spacer.
 7. The method of claim 6,wherein the inner spacers include at least one of silicon nitride andsilicon oxide.
 8. The method of claim 6, wherein the inner spacersinclude at least one of SiOC, SiOCN and SiCN.
 9. The method of claim 1,wherein in the etching a source/drain region of the fin structure, thefirst and second semiconductor layers of the source/drain region of thefin structure are etched.
 10. The method of claim 1, wherein in theetching a source/drain region of the fin structure, the firstsemiconductor layers of the source/drain region of the fin structure areselectively etched, thereby leaving the second semiconductor layersremaining.
 11. The method of claim 1, further comprising, after thesource/drain epitaxial layer is formed: removing the sacrificial gatestructure, thereby exposing a part of the fin structure; removing thefirst semiconductor layers from the exposed fin structure, therebyforming channel layers including the second semiconductor layers; andforming a gate dielectric layer and a gate electrode layer around thechannel layers, wherein the gate electrode layer is isolated from thesource/drain epitaxial layer by the inner spacer and the gate dielectriclayer.
 12. The method of claim 1, wherein: the first semiconductorlayers are made of SiGe, and the second semiconductor layers are made ofSi.
 13. The method of claim 1, wherein: the first semiconductor layersare made of Si, and the second semiconductor layers are made of SiGe.14. A method of manufacturing a semiconductor device, comprising:forming a first fin structure and a second fin structure, in both whichfirst semiconductor layers and second semiconductor layers arealternately stacked; forming a first sacrificial gate structure over thefirst fin structure and a second sacrificial gate structure over thesecond fin structure; while the second fin structure with the secondsacrificial gate structure are protected, etching a source/drain regionof the first fin structure, which is not covered by the firstsacrificial gate structure, thereby forming a first source/drain space;laterally etching the first semiconductor layers in the firstsource/drain space; forming a first inner spacer made of a dielectricmaterial on an end of each of the etched first semiconductor layers; andforming a first source/drain epitaxial layer in the first source/drainspace to cover the inner spacer, thereby forming a first structure;while the first structure is protected, etching the second semiconductorlayers in a source/drain region of the second fin structure, which isnot covered by the second sacrificial gate structure, thereby forming asecond source/drain space; laterally etching the second semiconductorlayers through the second source/drain space; forming a second innerspacer made of a dielectric material on an end of each of the etchedsecond semiconductor layers; and forming a second source/drain epitaxiallayer in the second source/drain space to cover the second inner spacer,thereby forming a second structure, wherein a lateral end of each of thefirst semiconductor layers has a V-shape cross section after the firstsemiconductor layers are laterally etched, and a lateral end of each ofthe second semiconductor layers has a V-shape cross section after thesecond semiconductor layers are laterally etched.
 15. The method ofclaim 14, wherein: in the etching the second semiconductor layers in asource/drain region of the second fin structure, the secondsemiconductor layers are selectively etched, thereby leaving the firstsemiconductor layers remaining, and the second source/drain epitaxiallayer wraps around the first semiconductor layers.
 16. The method ofclaim 14, wherein the lateral end of each of the first semiconductorlayers and the lateral end of each of the second semiconductor layershave a (111) facet of a semiconductor crystal, respectively.
 17. Themethod of claim 14, wherein the first semiconductor layers are laterallyetched by wet etching utilizing an HCl acid solution or a mixed solutionof NH₄OH, H₂O₂ and H₂O.
 18. The method of claim 14, wherein the secondsemiconductor layers are laterally etched by wet etching utilizing atleast one of an ammonium hydroxide (NH₄OH) solution andtetramethylammonium hydroxide (TMAH) solution.
 19. The method of claim14, wherein: sidewall spacers are formed on side faces of the firstsacrificial gate structure and on side faces of the second sacrificialgate structure, and wherein sidewall spacers are made of a differentmaterial than the first and second inner spacers.
 20. A semiconductordevice, comprising: semiconductor wires disposed over a substrate, eachhaving a channel region and a source/drain region; a source/drainepitaxial layer in contact with and wrapping around the source/drainregion of each of the semiconductor wires; a gate dielectric layerdisposed on and wrapping around each channel region of the semiconductorwires; a gate electrode layer disposed on the gate dielectric layer andwrapping around the each channel region; and insulating spacers disposedin spaces, respectively, the spaces being defined by adjacentsemiconductor wires, the gate electrode layer and the source/drainregion, wherein each of the insulating spacers has a triangular or awedge-shaped cross section.